He was the son of William Rainsborough, a captain and Vice-Admiral in the Royal Navy who had previous marriage links to Massachusetts. He was raised in Wapping and before the war traded in currants with the Turkey Company and invested money in Ireland.Thomas Rainsborough was devout in his religious beliefs and was a Fifth Monarchist. (The Fifth Monarchists or Fifth Monarchy Men were an extreme Puritan sect particularly active from 1649 to 1660 during the Interregnum and took their name from a prophecy in the Book of Daniel that four ancient monarchies (Babylonian, Persian, Macedonian, and Roman) would precede the kingdom of Christ). On his father’s death he inherited some property in Southwark and a £1,000 so he was a well to do gentlemen.
Rainsborough served in the Parliamentary forces during both the first and second English Civil Wars. Originally a naval officer he commanded the Swallow, the Lion and other English naval vessels during the first civil war. By May 1645, he was a Colonel in the New Model Army having raised an infantry regiment. Rainsborough took an active part in the battles at Naseby and Langport. In 1645 he captured the symbolic stronghold of Berkeley Castle for Parliament before moving to the siege of Oxford, which surrendered the following June. Later in 1646, he helped conclude the Siege of Worcester and was made the city’s governor.
In January 1647, Rainsborough became an M.P. for Droitwich. He was part of the delegation that presented the armies “Heads of Proposals” to Charles 1. He left early and went back to his troops spreading the words of the King’s instrangence. Rainsborough was the most senior member of the Army Council to support the Leveller proposals. (The Levellers were committed to popular sovereignty, extended suffrage, equality before the law and religious tolerance). During the Putney Debates his arguments for universal suffrage were called ‘anarchy’ by Henry Ireton, who spoke for the Army Grandees. Rainsborough was at loggerheads with Cromwell and led him to thunder about both of them “one of them must not live”. Cromwell thought Rainsborough would do nothing but by the sword and Rainsborough could not understand Cromwell’s persistence in negotiating with the King!
In 1648 Rainsborough was moved from the army and given,( by Parliament but only on a 88-66 vote with the support of Cromwell), command of the navy,(getting him out of the way), holding the rank of Vice-Admiral. His appointment was unpopular with both officers and sailors, resulting in a mutiny (and declaration for the King) of six ships on 27 May 1648. In the same year he briefly replaced the Royalist sympathiser William Batten as Captain of Deal Castle, but was dismissed when the castle also declared for the King. Despite his previous experience, Rainsborough was viewed by the navy as being too radical and having been imposed on them by the army. As a result of the mutiny the Earl of Warwick was appointed Lord High Admiral, with Rainsborough returning to the army. On his return to the army, Rainsborough led the siege and victory at Colchester.
In October 1648, Rainsborough was sent by his commander, Sir Thomas Fairfax, to the siege at Pontefract Castle. Whilst he was in nearby Doncaster, he was killed by four Royalists during a bungled kidnap attempt. They broke in with the view to ransoming him for a senior Royalist, they had forged orders from Cromwell, but he broke free, dashed out into the street drawing his sword and in the ensuing fight was run through. The site is still marked today by a plaque outside of the House of Fraser. As Rainsborough was under Cromwell’s disfavour and there were tensions between Rainsborough and the commander he was displacing, Henry Cholmely, who later defected to the Royalists, many at the time wondered whether there was some Parliamentary complicity in his death, as do historians today, as Rainsborough had been one of the first to call for the trial of the King . However Royalist Propaganda may also have played a part in all the rumours. Cromwell certainly took pains to track down and punish the offenders
His funeral was the occasion for a large Leveller-led demonstration in London. 3,000 mourners wearing the Levellers’ ribbons of sea-green and bunches of rosemary for remembrance in their hats marched through the City to Wapping. He was buried in St John’s Churchyard, beside his father
He married Margaret and they had a son William and another unidentified child. Little is known of her but on his death Parliament paid his arrears of pay and granted her a pension and some land in the west country. Rainsborough is the most prominent of the Leveller martyrs. In May 2013 a plaque was unveiled by Clr Rania Khan, John Rees, a writer and left wing political activist) and Tony Benn (former MP) in memory of Rainsborough at St John’s, Wapping
(Wikipedia, Spartacus Educational, D.N.B, Antonia Fraser)